Closteroviridae

VIRION

Non-enveloped, flexuous and exceptionally long, filamentous particles about 950-2200 nm in length and 10-13 nm in diameter. The virion body is assembled by the major capsid protein (CP) and the tail by the minor capsid protein (CPm).

GENOME

Mono-(Ampelovirus, Closterovirus) or bi-partite (Crinivirus), linear ssRNA(+) genome of 15 to 20 kb. 3' terminus has no poly(A) tract and the 5' terminus probably has a methylated nucleotide cap.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. ORF1a and ORF1ab protein (containing RdRp) are produced by ribosomal frameshifting. Other ORFs are translated from a set of nested 3' co-terminal subgenomic RNAs.

REPLICATION

CYTOPLASMIC

Virus penetrates into the host cell.

Uncoating, and release of the viral genomic RNA into the cytoplasm.

The viral RNA is translated into a processed ORF1 polyprotein to yield the replication proteins.

Replication occurs in viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).